Electric discharge lamps



Oct. 29, 1957 H. G. MOLYNEUX ELECTRIC DISCHARGE LAMPS 2 Sheets-Sheet 1Filed June 22, 1956 Oct. 29, 1957 H. G. MOLYNEUX 9 ELECTRIC DISCHARGELAMPS Filed Juhe 22, 1956 2 Sheets-Sheet 2 United States Patent ELECTRICDISCHARGE LAMPS Harold Grosvenor Molyneux, Ribbleton, lreston, England,assignor to Siemens Edison Swan Limited, a corporation of Great BritainApplication June 22, 1956, Serial No. 593,208

Claims priority, application Great Britain July 1, 1955 1 Claim. (Cl.315-49) The present invention relates to mercury vapour electricdischarge lamps and more especially to lamps emitting ultra-violet raysfor medical treatment and which are suitable for domestic use. Suchlamps may be used domestically for producing a tanning effect of thehuman skin.

It is well known that mercury vapour electric discharge lamps emiterythemal radiation which in the shorter wave lengths (e. g. theemission at a wave length of 2537 Angstrom units) may be harmful unlessspecial precautions are taken and this radiation is present not onlyduring the normal operation or the lamp but also during the running upperiod. In the lamp of the present invention the amount of harmfulradiation is reduced both in the normal operation of the lamp and duringits running up period without reducing to an appreciable extent thebeneficial longer wave ultra-violet radiation (e. g. the emission at awave length of 3650 Angstrom units).

According to the present invention, there is provided a mercury vapourelectric discharge lamp in which the discharge tube proper is shieldedto a partial but significant degree, so far as external objectsirradiated by the lamp are concerned, by a shielding member composed ofmaterial that is transparent to radiation of wave lengths in a widerange extending from about 3000 Angstrom units upwards and including3650 Angstrom units, but is substantially opaque to radiation of wavelengths in a wide range below 3000 Angstrom units and including 2537Angstrom units. The shielding member serves to filter out a portion ofthe lower wave length erythemal radiation emitted by the discharge tube.A suitable material for this shielding member is the glass known underthe trade name Pyrex.

The shielding member is in the form of a helix surrounding, but spacedfrom, the discharge tube proper. With a shielding member of this form,the proportion of the total lower wave length erythemal radiation fromthe discharge tube which is rendered ineffective can readily be made tohave a desired value by suitable choice of the dimensions of the memberwhich is coiled to form the helix and of the diameter and pitch of thehelix. The dimensions of the helix may suitably be such thatapproximately one half the surface of the discharge tube proper isobscured when the lamp is viewed from the front.

The shielding member is in the form of a helix which surrounds thedischarge tube proper and which is constituted by a coiled tube, andthis coiled tube has running through it a length of resistance wireconstituting a ballast resistance for the discharge tube, and the helix,although spaced from the discharge tube, surrounds the discharge tubesufficiently closely for the heat generated in said ballast resistanceto shorten materially the time taken for the discharge tube to run up tothe full discharge condition when the lamp is switched on. The

2,811,671 Patented Oct. 29, 1957 specific material previously mentionedas being suitable for the shielding member is especially suitable, sinceit is such as to withstand the heat dissipated by the discharge tubeproper and the ballast resistance.

By way of example, a'specific embodiment of the invention will now bedescribed with reference to the accompanying drawings. The embodimentconcerned takes the form of a mercury vapour electric discharge lamp formedical treatment, the lamp being one provided with a shielding memberconstituted by a coiled tube, and this coiled tube containing a ballastresistance for the discharge tube proper. Fig. 1 of the drawings shows afront elevation of the lamp, Fig. 2 shows a side elevation, and Fig. 3shows a plan. The lamp has a base member 1 of insulating material whichis provided at its four corners with bolts 2 and nuts 3. The bolts 2 andnuts 3 enable the lamp to be suitably mounted for use. Supported abovethe base 1, by suitable supporting and electrical conducting members 4and 5 securely fixed in this base, and various auxiliary supportingmembers, are the mercury vapour discharge tube proper 6 and theshielding member 7. The shielding member 7 is formed of a tube of theglass known under the trade name Pyrex, and contains a ballastresistance 8 which is connected in series with the discharge tube 6 andconsists of a coiled length of resistance wire of the kind known asNichrome. Two terminal arrangements 9 and 10 are connected to themembers 4 and 5 respectively by the members It and 12 respectively. Areflector 13 is supported by two members 14 and 15 securely fixed in thebase 1. The shielding member 7, although spaced from the discharge tube6, surrounds the latter sufliciently closely for the heat generated inthe ballast resistance 8 to shorten materially the time taken for thedischarge tube to run up to the full discharge condition when the lampis switched on. The discharge tube 6 takes the form of a conventionall25-watt tube about 5 cms. in length, and the shielding member 7 inwhich the ballast resistance is contained is a tube of approximately 5millimetres bore wound in the form of a helix having a diameter of 2cms. with the turns spaced 1 cm. apart. With a suitable ballastresistance such a lamp may be operated directly from 200250 volt mains.

What I claim is:

A mercury vapor electric discharge lamp in which the discharge tubeproper is shielded to a partial but significant degree, so far asexternal objects irradiated by the lamp are concerned, by a shieldingmember composed of material that is transparent to radiation of wavelengths in a wide range extending from about 3000 Angstrom units upwardsand including 3650 Angstrom units, but is substantially opaque toradiation of wave lengths in a wide range below 3000 Angstrom units andincluding 2537 Angstrom units, said shielding member comprising a helixsurrounding the discharge tube and spaced therefrom, the helixconstituting a coiled tube, and a length of resistance wire in saidcoiled tube, the resistance wire constituting a ballast resistance forthe discharge tube, and said helix surrounding the discharge tubesufiiciently closely for the heat generated in said ballast resistanceto shorten materially the time taken for the discharge tube to run up tothe full discharge condition when the lamp is switched on.

References Cited in the file of this patent UNITED STATES PATENTS2,355,258 Biggs et a1. Aug. 8, 1944 2,362,384 Libby Nov. 7, 19442,434,980 Bilofsky Jan. 27, 1948 2,658,984 Mohn Nov. 10, 1953

